1. Field of the Invention
This invention relates to an evacuated double-tubing type solar heat collector including an inner tube and an outer tube which is, in particular, designed to reduce or eliminate the possibilities of the inner tube being broken due to external vibrations.
2. Description of Background Information
A variety of solar heat collectors are well-known in the art. A representative evacuated double-tubing type solar heat collector, which is currently the most effective in view of heat absorption, includes an elongate outer glass tube into which an elongate inner glass tube is inserted. The inner glass tube includes a selective absorption film applied over its surface and the space between both tubes is evacuated to a high degree of vacuum.
However, with this type of solar heat collector it is likely that the inner tube may vibrate within the outer tube during transportation or handling. In view of the fact that the least careless handling of the solar heat collector may cause deflection of the inner tube within the outer tube, cracking or breakage takes place at the junction of the open end portions of both tubes. The junction between the inner and outer tubes is most susceptible to deflection. As a result, the insulating layer of vacuum is exposed to the ambient air and the collector does not work at all. This problem is primarily attributable to the fact that both tubes are formed of an elongate, hollow glass material.
Another problem with a conventional collector is that, as shown in FIG. 1, an outer tube 1 is provided at a point near its base end with a centripetally projecting dimple 3, whicn functions as a spacer for keeping the tube 1 away from an inner tube 2 at a given interval. The dimple 3 serves as a spacer to some degree, but cannot possibly absorb the vibration of the tube 2 due to the fact that the dimple 3 is formed of a glass material (a rigid material) from which the tube 2 is formed. Hence, the vibration of the inner tube 2 gives rise to a rattling noise and, eventually, leads to breakage of a junction 4 between the outer tube 1 and the inner tube 2 as referred to above.